I think I've just stumbled close to the truth but I need to study a little further. In 1968, Johnny Rutherford, a future three-time winner of the Indy 500 drove car #96 in five races on the USAC Indy car circuit that year, and crashed in two of them once at Hanford, CA and then at Phoenix. The other car seen in the footage in "Uncle Kevin" before the crash is car #5, and that year #5 was the car of Al Unser (who went on to win four Indy 500s). The Phoenix crash is described as an incident where Unser's engine blew and dumped oil and Rutherford spun and crashed and then several other cars piled into Rutherford causing a more serious fire. Rutherford was pulled out with burns on his hands. This is *close* to what we see in the footage except there should be other cars hitting #96 before the big explosion I think. I can't find an independent film of the Phoenix race yes for confirmation but this is so far a good possibility. The USAC race charts for 67 or 69 might yield something even more definite but I think this is definitely footage from a USAC Indy race.